It is common practice to introduce chemical preservatives into cosmetic or dermatological compositions, these preservatives being intended to combat the growth of microorganisms in these compositions, which would otherwise make them unsuitable for use. It is in particular necessary to protect compositions against microorganisms capable of growing inside the composition and also against those which the user might introduce therein while handling it, in particular when taking up products in jars with the fingers.
The effectiveness of the preservatives conventionally used is variable and their formulation can pose problems of formulation, such as of incompatibility, or even of destabilization, in particular of emulsions. Furthermore, they may be the cause of undesirable side effects (irritation, allergy) in particular on consumers with sensitive skin. Thus, chemical preservatives commonly used are in particular parabens and formaldehyde-releasing compounds; but these preservatives have, however, the drawback of causing irritation, in particular on sensitive skin, when they are present at relatively high levels. Other known preservatives are organic hydroxy acids; but they may also give rise to irritation due to their desquamating effect on the skin, which is not always well tolerated.
Many conventional preservatives such as, for example, parabens, are constantly being scrutinized due to negative media attention and/or changes in regulatory or safety requirements. In response thereto, formulators have increasingly turned to the use of alcohol (ethanol) as a biocide to protect cosmetic products from microbial spoilage. However, to be an effective biocide, a high concentration of ethanol must be used in the formulas. Unfortunately, high concentrations of ethanol render the manufacture and handling of such products hazardous. Moreover, high levels of said alcohol also result in consumer-perceived drying of skin.
In response to the above-referenced drawback associated with the use of ethanol, formulators have also turned to the use of glycols having mid-sized alkyl chain lengths for their anti-microbial activity. Mid-sized alkyl chain glycols comprise glycols having C5 to C12 alkyl chains, such as, for example, pentylene glycol, hexylene glycol, caprylyl glycol, and decylene glycol, and mixtures thereof. However, the surface-active properties of these glycols, most often, also cause the instability of an emulsion, particularly for water-in-oil (W/O) emulsions. These glycols tend to possess surfactant-like properties which in turn have a negative effect on the composition in view of being present in the form of an emulsion, thereby resulting in the emulsion becoming unstable.
Inverse (W/O) emulsions are notoriously difficult to preserve due to the fact that microorganisms can be lodged in the external, continuous oil phase, making it difficult for the preservative ingredients to counteract. Thus an effective preservation system is imperative to provide adequate product protection and ensure consumer's safety.